Method of filtering a subterranean fluid from a well bore using a resin bonded well liner

ABSTRACT

An apparatus and method of manufacturing a prepacked resin bonded well liner comprised of bonding granular particles to a perforated pipe. The granular particles are coated with a partially polymerized resin that is hard and tacky to the touch. Upon the introduction of heat, the polymerization proceeds, curing the resin into an insoluble and infusible cross-linked state. The contact regions between the adjacent particles bond the packed particles into a porous and permeable matrix.

This is a divisional of application Ser. No. 08/311,577 filed on Sep.23, 1994, now U.S. Pat. No. 5,500,174.

BACKGROUND

The present invention generally relates to apparatus for filtering andscreening particulate matter in downhole wells, and, more particularly,to an improved method of manufacturing a prepacked well liner forfiltering unconsolidated material out of inflowing well fluid such aswater, oil or gas.

In the course of completing an oil and/or gas well, it is commonpractice to run a string of casing into the well bore and then to runthe production tubing inside the casing. At the well site, the casing isperforated across one or more production zones to allow productionfluids to enter the casing bore. During production of the formationfluid, formation sand is also swept into the flow path. The formationsand is relatively fine sand that erodes production components in theflow path. In some well completions, the well bore is uncased, and anopen face is established across the oil or gas bearing zone. Such openbore hole arrangements are utilized, for example, in water wells, testwells, and horizontal well completions.

It is generally known that the production of fluids from an undergroundproducing formation is often reduced or is completely chocked off by themovement of sand and/or other finely divided solid materials into thewell bore. Sand and finely divided solids are also troublesome when theyare entrained in the producing fluids because of abrasion of pump partsand other equipment.

It is a general practice to employ strainers or screening devices toovercome the above noted problems. A wide variety of well filter deviceshave been devised to prevent the movement of sand and other materialsinto the producing zone of wells. Such devices usually consist of aperforated metal mandrel generally employed in association with a finemesh screen. The perforated metal mandrel and fine mesh screen areinstalled in the flow path between the production tubing and theperforated casing (cased) or the open well bore face (uncased). In aprocedure called gravel packing, the annulus around the screen is packedwith a relatively coarse sand or gravel which acts as a filter to reducethe amount of fine formation sand reaching the screen. The gravel andsand, which is often called a proppant, is pumped down the well in aslurry of water or gel. In well installations in which the screen issuspended in an uncased open bore, the gravel pack further supports thesurrounding unconsolidated formation.

A problem, which arises during initial production following the gravelpacking operation, is that fine sand may be carried through the gravelpack before the gravel pack stabilizes. It is not unusual to produce asubstantial amount of fine sands before the gravel pack finelyconsolidates and yields clean production. After gravel packing andduring the early stages of well production, these fines tend to migratethrough the gravel packing and screen and lodge within the inner annulusbetween the wire wrap and the perforated mandrel. In some instances,this can cause severe erosion of the screen and ultimate failure of thescreen to reduce sand invasion. In other situations, the sand fines mayinclude plugging materials which can completely plug the mandrel flowpassages and terminate well production shortly after completion. In deepwells, when the screen becomes plugged and the pressure in theproduction tubing is reduced, the formation pressure can collapse thescreen and production tubing. Moreover, when a substantial amount ofsand has been lost from the surrounding formation, the formation maycollapse with a resultant damage to the well casing or liner andconsequent reduction or termination of production.

A further problem with gravel packing is that gravel packed liners candeteriorate over time and can be difficult to replace because removalfrom the well bore can cause the metal screen to become entangled orbroken during removal from the well. Gravel packing can also create anon-uniform filter in high angle and horizontal wells due to thedifficulty in the proper placement of the sand or gravel with currentpacking techniques. Additionally, the gravel packing procedure is bothexpensive and complicated.

One attempt to overcome the foregoing problems of gravel packing hasbeen to interpose a prepack of bonded proppant between the perforatedmandrel and the perforated casing or the open well bore face. The meshwire screen is replaced by a permeable filter body of granular material,for instance gravel, which is cemented together by a binding agent whichis insoluble by water or other liquid to be filtered and which ispermanently adhered to the perforated pipe. See, for example, U.S. Pat.No. 2,843,209 issued to W. Degen and U.S. Pat. No. 3,361,203 issued toR. Rensvold which are incorporated herein by reference. The bindingagent is typically an artificial resin such as a thermoplastic orthermosetting resin such as phenol formaldehyde, urea formaldehyde ormelamine formaldehyde. The grain size of the gravel or sand is adaptedto the soil conditions surrounding the filter which may be uniform or itmay comprise several layers containing different binders and proppants.

Unfortunately, the process lacks control in the ability to provideuniform interstitial spaces between proppant grains. During the curingprocess the resin remains free flowing thereby allowing the resincoating to flow into the interstitial regions between proppant grains.The resin in the proppant interstices results in random plugging of thepore spaces during the curing process. This has resulted in suchdiminished porosity and permeability of the well filter that such wellliner has not continued in general use in the well drilling industry.

An attempt to overcome the problems of resin plugging of a prepackedliner is disclosed in U.S. Pat. No. 3,683,056 issued to Brandt et al.The resin bonded particles are cured in a mixture of hot wax to causethe bonding agent to polymerize and consolidate the particle pack whileallowing the wax to cool in and around the particle pack and in theinterstitial regions between contiguous particles. Once the prepackedliner is installed in the well, the formation heat causes the wax tomelt and be removed from the prepack thereby providing for a porous andpermeable matrix of resin bonded particles. Unfortunately, the subjectmethod is not suitable where formation temperatures are insufficient tomelt the wax disposed in the interstitial regions of the matrix.Furthermore, the wax procedure is both expensive and complicatedinvolving complicated machinery to pump and mix the molten wax bath.

SUMMARY

The present invention addresses the aforementioned disadvantages byproviding an improved method of manufacturing a prepacked well linerthat achieves increased porosity and permeability and accordingly, anincrease in fluid flow from a downhole well. The manufactured prepackedwell liner consists of a perforated pipe which is coated by a permeablegranular material, often referred to as a proppant, which functions as afilter. The granular material is cemented together by a binding agentwhich is insoluble by water or other liquid to be pumped and filtered toform a porous annulus which is permanently adhered to the perforatedpipe. The grain size of the granular material may be adapted to the soilconditions surrounding the filter.

In a preferred embodiment of the present invention, a base pipe ismachined to include a plurality of apertures. The apertures arelongitudinally and radially spaced to provide for fluid communicationtherethrough. The base pipe is further formed with each extremitythreaded. In this manner, the base pipe is capable of being coupled toadditional base pipes to provide for an extensible production pipe. Aninner mold is then positioned in the interior bore of the base pipe. Theinner mold is configured as a cylinder having a diameter substantiallyequal to the bore of the base pipe and a length substantially equal tothe length of the base pipe. The inner mold thereby effectivelyrestricts any particulate materials, particularly the proppant, fromflowing into the inner bore of the base pipe from the exterior of thebase pipe during the manufacturing process.

Likewise, an outer mold is also employed to shape the proppant duringthe manufacturing method of the present invention. The outer moldincludes a cylindrical inner bore of a diameter greater than thediameter of the base pipe. The bore terminates at each of itsextremities in an end plate which is formed with a circular orificedisposed concentric with the outer mold bore and having a diameter equalto the outer diameter of the base pipe. The outer mold is further slitthe length of the outer mold along the axis of the bore to form twoouter mold halves which are joined lengthwise by a hinge in clamshellmanner. During the manufacturing process of the present invention, thebase pipe is positioned in the outer mold with its extremitiestelescoping through the endplate orifices to form an annulus between thebase pipe and the outer mold.

Once the inner mold has been inserted into the base pipe and the outermold has been positioned around the base pipe, the annulus is filledwith resin coated particles. The resin coating the particles is apartially polymerized thermosetting resin which forms a nontacky coatingsuch that the proppant remains free flowing at ambient temperatures. Theresin is reactive at higher temperatures, however, to soften and thencure into an infusible cross linked state. During the method of thepresent invention, the entire mold assembly, including the base pipe,inner and outer molds, and resin coated particles is heated torecommence polymerization of the resin coating. Initially, the resin inthe annulus fuses and unites at the contact areas between contiguousparticles. As the temperature increases, polymerization proceeds untilthe resin is cured into an insoluble and infusible cross-linked state.The contact regions between the adjacent particles bond the packedparticles into a permeable network having considerable strength.

The assembly is allowed to cool whereupon the inner and outer molds areremoved from the base pipe and pre-bonded particles, to provide aprepacked resin bonded well liner having improved porosity and reducedmanufacturing costs.

The method of present invention overcomes the impediments of priorprepacked well liners by partially polymerizing the thermosetting resinprior to the mold process. Prior to filling the mold assembly, the resinis partially polymerized to the particles to create a nontacky surfacethat is hard to the touch at ambient temperatures. This enables theparticles to remain free flowing and inconglomerate while beingpositioned in the mold assembly. Further, the nontacky properties of thethermosetting resin inhibits the flow of the resin into the particleinterstices during the heating procedure. However, because the resin isonly partially polymerized, the resin fuses and unites at contact areasof contiguous particles. The partial polymerization thus alleviates theproblems associated with resin flowing into the interstitial areasbetween contiguous particles which plug the liner during the moldingprocess. In this manner, the present invention is a high strengthprepacked well liner with improved porosity and improved well pumpingcapabilities.

The present invention also overcomes the handicaps of gravel packingwhich usually comprises a perforated metal pipe concentrically mountedinside a steel wire wrap screen. The present invention does not requirethe complex procedure of packing a granular slurry of water and proppantinto the annular space around the perforated mandrel at the well site tointroduce the filter. Further, steel wire wrapping is not needed toposition the proppant in place around the perforated mandrel. Thiseliminates the difficulties associated with a steel wire wrapping whichis costly and susceptible to tearing. The method of the presentinvention produces a resin bonded well liner that is less susceptible todamage than a liner employing a steel wire wrapping because there is nowire which can entangle or break. Accordingly, there is no concern thatthe broken or entangled screen will release the proppant down the well.Further, the present invention is economically superior to conventionalliners because the prebonded proppant eliminates the need for anexpensive wire wrapping.

The present invention also ensures a completely uniform liner in highangle wells. Presently, when employing current packing techniques, highangle and horizontal wells present difficulty in the proper placement ofthe proppant, often leaving voids. Because the method of the presentinvention manufactures the liner and proppant assembly prior tointroduction into the well, uniform proppant bonding can be effected.

It is an object of the present invention to provide a method ofmanufacturing a prepacked bonded well liner that has increased porositywith respect to previously manufactured prepacked well liners.

It is an additional object of the present invention to provide a methodof manufacturing a prepacked bonded well liner that does not include awire wrap. The present method of manufacturing being both simplistic andinexpensive.

Further, is an object of the present invention to produce a prepackedbonded well liner that has high strength and is suitable for thepressures and temperatures of a downhole well.

Other features and advantages of the present invention will beappreciated by those skilled in the art upon reading the detaileddescription which follows with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood with regard to the followingdescription, appended claims, and accompanying drawings where:

FIG. 1 is a cross-sectional view of the free flowing resin coatedparticles of the present invention;

FIG. 2 is a cross-sectional view of the resin coated particles bonded ina cross-linked state;

FIG. 3 is a side view of the base pipe of the present invention;

FIG. 4 is a cross-sectional view of the base pipe of FIG. 3;

FIG. 5 is an expanded view of the mold assembly and base pipeillustrating the preferred embodiment of the present invention;

FIG. 6 is a cross-sectional view of the mold assembly and base pipeillustrating the preferred embodiment of the present invention;

FIG. 7 is a cross-sectional view of the mold assembly and base pipe ofFIG. 5;

FIG. 8 is a cross-sectional view of the mold assembly and base pipe ofFIG. 6;

FIG. 9 is a cross-sectional view of the resin coated particle beingformed around the base pipe illustrating a preferred embodiment of thepresent invention;

FIG. 10 is a cross-sectional view of the resin coated particles beingformed around the base pipe of FIG. 9;

FIG. 11 is a side view of the mold assembly and base pipe illustrating apreferred embodiment of the heating operation of the present inventionin which the mold assembly, resin coated particles and base pipe areheated in an oven;

FIG. 12 is an expanded view of the mold assembly and prepacked wellliner illustrating the removal of the mold assembly;

FIG. 13 is an expanded end view of the mold assembly and prepacked wellliner illustrating the removal of the mold assembly of FIG. 12;

FIG. 14 is a longitudinal view of the prepacked well liner of thepresent invention;

FIG. 15 is a cross-sectional view of the prepacked well liner of thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

While the present invention is susceptible of embodiment in variousforms, there is shown in the drawings and will hereinafter be describeda presently preferred embodiment of the invention, with theunderstanding that the present disclosure is to be considered as anexemplification of the invention, and is not intended to limit theinvention to the specific embodiment illustrated.

The present invention provides for an apparatus and an improved methodfor manufacturing a prepacked well liner, as shown generally in FIGS. 14and 15. Referring to FIGS. 3 and 4, a base pipe 10 comprising a robe 9having a concentric bore 12 is machined to include a plurality ofapertures 14 thereby defining inner portals 16 and outer portals 17 inthe base pipe inner and outer sidewall 18 and 19, respectively. The basepipe may be of any length, with maximum lengths of 40 feet generallyaccepted in the art. Machining may be effected by boring, drilling,cutting, or any other machining process to create apertures such asholes or slots which are longitudinally and radially spaced along thelength of the base pipe. As is standard in the art, each extremity ofthe base pipe is threaded to allow the base pipe to be coupled to likebase pipes to provide an extensible well liner.

Referring to FIGS. 5, 8 and 10, the method of the present inventionfurther employs an inner mold 20 which restricts the flow of particulatematter through the base pipe apertures 14 during the manufacturingprocess. The inner mold is positioned in the base pipe bore 12 andfunctions to restrict the flow of proppant through the apertures 14 andinto the base pipe bore while forming the proppant 70 into an annularfilter to be bonded to the cylindrical surface of the base pipe. In apreferred embodiment, the inner mold is configured as a cylinder havinga diameter equal to the inner diameter of the base pipe and a lengthsufficient to block the base pipe apertures once the inner mold has beeninserted into the bore 12 of the base pipe. Once the inner mold is inplace, the exterior cylindrical surface 22 of the inner mold engages theinner portals 16 of the apertures 14 thereby obstructing passagetherethrough. In this manner, the previously open apertures formcavities 15 in the base pipe originating at the outer portals andterminating at the surface of the inner mold as shown in FIG. 10.

Similarly, an outer mold 26 is employed to shape the proppant filter bypositioning the base pipe 10 and inner mold 20 into the outer mold, asshown in FIGS. 5, 6 and 7. In a preferred embodiment, the outer moldincludes a cylindrical inner bore 27 of a diameter greater than thediameter of the base pipe. In a preferred embodiment, a pipe 28, havinga diameter larger than the outer diameter of the base pipe and having alength less than the length of the base pipe, functions as the inner andouter sidewalls 30 and 32, respectively, of the outer mold. The outermold pipe is slit along its length to form two opposing pipe halves, 34and 36, respectively. The two halves are joined lengthwise in clamshellfashion to allow the simplistic installation and removal of the outermold from the base pipe. The outer mold further includes endplates 38and 40, respectively, at the outer mold extremities to form acylindrical cavity 42 internal to the outer mold. As would beappreciated in the art, the endplates may be integrated or detachablewith the outer mold pipe.

In a detachable embodiment, the endplates 38 and 40 are configured ascircular plates 44 having an annular ring 46 extending from the circularplate's periphery. The inner diameter of the annular ring corresponds tothe outer diameter of the outer mold pipe 28 such that an extremity ofthe outer mold pipe telescopes into the annular ring to engage theendplate circular plate. In this manner, when the endplates are affixedto the outer mold pipe, the outer mold bore terminates at itsextremities at the endplates, thereby forming a cylindrical cavity 42within the outer mold. The endplates further include a concentriccircular orifice 48 of a diameter substantially equal to the diameter ofthe base pipe 10. As discussed below, during the manufacturing processof the present invention, the base pipe, having the inner mold 20configured internal to the base pipe bore 12, is positioned into theouter mold cavity 42 with the extremities of the base pipe telescopingthrough the endplate orifices 48 to form an annulus 50 between the basepipe 10 and inner sidewall 30 of the outer mold pipe 28, as shown inFIG. 8.

Referring to FIGS. 1 and 2, the method of the present invention alsoemploys proppant 70 comprising particles 72 coated with resin 74. Theproppant is formed into a filter to screen and prevent the entry intothe base pipe of sand and other finely divided solids from the producingformation. The proppant may be any particulate of any size suitable forthe surrounding formation. Particles from 6 to 200 mesh (U.S. StandardSieve) are generally used. The choice of the particulate is governed bythe properties of the cured mass. For example, in the oil and gasindustry extremely high strength proppants are needed to hold openformation fractures. In such an application, the present invention mayuse glass beads as the particulate substrate. Also used as proppantswhere stresses are very high, are sintered bauxite, aluminum oxide,ceramics and other mineral particulates may be coated. Also suitable foruse as particulates are various organic materials such as walnut andpecan shells, synthetic polymers such as nylon, polyethylene and otherresin particles. Metallic particles such as steel and aluminum pelletsor shavings can also be coated.

The resin coating the proppant is generally any resin capable of beingcoated on the particle and then being cured to a higher degree ofpolymerization. Examples of such resins include phenol-aldehyde resinsof both the resole and novolac type, urea-aldehyde resins, melaminealdehyde resins, epoxy resins and furfuryl alcohol resins. The resinsmust form a solid nontacky coating at ambient temperatures. This isrequired so that the proppant remains free flowing under normal storageconditions prior to heating. With reference to FIGS. 1 and 2, upon theintroduction of heat, the resin 74 fuses and unites at the contactsurfaces of contiguous particles 72. Because the resin has beenpartially polymerized, the resin does not free flow into theinterstitial areas 78 between contiguous particles during the heatingprocess. The interstitial areas remain open, thereby maintaining theporosity of the proppant filter and providing for a filter withincreased interstitial regions and having the capacity for improvedfluid flow. The interstitial regions are small enough, however, tofilter and screen sand and finely divided solids disposed in the fluid,from flowing through the proppant filter.

A preferred embodiment of the resin coated proppant is produced bySantrol Products, Inc. under the tradename Super HS, and Super Sand. Theresin coated proppant is manufactured to the methods disclosed in issuedU.S. Pat. Nos. 4,518,039, 4,585,064, 4,597,991, 4,732,920, and 4,888,240which are hereby incorporated by reference.

Referring to FIG. 5, in a preferred embodiment of the present invention,the cylindrical inner mold 20 is positioned in the inner bore 12 of thebase pipe 10 to block the base pipe apertures 14 and particulatecommunication therethrough. A first endplate 38 is then press fit to afirst extremity of the outer mold pipe 28, as shown in FIG. 6. Once thefirst endplate has been affixed, the base pipe and integrated inner moldare concentrically inserted into the outer mold bore 27 with a firstextremity of the base pipe telescoping through the orifice 48 of thefirst endplate. Thereafter, the assembly is positioned vertically withannular space 50 between the base pipe and outer mold positionedlongitudinally.

Referring to FIG. 9, once positioned, the annulus 50 between the basepipe and outer mold sidewall is filled with resin coated proppant 70.Filling may be controlled by simply pouring or pumping the resin coatedproppant into the annulus. Thereafter, the second endplate 40 is affixedto the second extremity of the outer mold pipe 28 with the secondextremity of the base pipe 10 telescoping through the concentric orifice48 of the second endplate. The entire mold assembly 84 is then heated inan oven 82, as illustrated in FIG. 11. Referring also to FIGS. 1 and 2,upon the introduction of heat, the resin coating the proppant softensand unites at the contact areas 76 between contiguous particles 72 whilemaintaining the interstitial areas 80 between particles. As thepolymerization proceeds, the resin cures into an insoluble and infusiblecross-linked state. The contact regions between the adjacent particlesbond the packed particles into a highly permeable network ofconsiderable strength.

In a preferred embodiment of the heating operation of the presentinvention, the mold assembly is heated to 300° F. for six hours. Theassembly is then allowed to cool, and the inner and outer molds areremoved, as illustrated in FIGS. 12 and 13. As one in the art wouldappreciate, the inner mold 20 may be removed by simply sliding the innermold from the base pipe bore 12. Further, once the endplates 38 and 40,respectively, have been removed from the outer mold pipe 28, the two panconfiguration of the outer mold allows the well liner to be easilyremoved. Though the inner and outer molds may be easily removed from theresin bonded proppant, the resin bonded proppant remains securelyaffixed to base pipe. The resin between the base pipe and contiguousparticles bonds the cross-linked resin coated proppant to the base pipe.Further, referring to FIGS. 14 and 15, when the free flowing resincoated particles are poured into the annular space 50 between the outermold and the base pipe, the resin coated proppant forms projections 80into the cavities 15 of the base pipe 10. Therefore, once cured, anyattempt at removing the resin bonded proppant from the base pipe isrestricted by the proppant projection's resistance to shearing. As shownin FIGS. 14 and 15, a high strength prepacked well liner with improvedporosity and improved well pumping capabilities is thereby provided. Theresin coated proppant has enlarged interstitial regions while, stillrestricting the flow of solids into the base pipe bore 12. The prepackedwell liner may then be introduced into a well bore to effect thefiltering and production of subterranean fluid.

Although the method of the present invention has been described withreference to preferred embodiments, workers skilled in the art willrecognize that changes may be made in form and detail without departingfrom the spirit and scope of the invention.

What is claimed is:
 1. A method of filtering subterranean fluid from a well bore, comprising:forming a plurality of apertures into a base pipe to form a perforated pipe, said base pipe being substantially cylindrical in configuration with a concentric first bore disposed along the axis thereof to define a tubular sidewall, said apertures longitudinally spaced and formed radially therethrough; positioning said perforated pipe in an outer mold, said outer mold having a second bore of a diameter larger than the outer diameter of said perforated pipe, said perforated pipe positioned to form a space between said outer mold and said perforated pipe; filling said space with particles, said particles being coated with resin which is partially polymerized to form a nontacky coating upon said particles such that said particles remain free flowing at ambient temperatures, said resin being reactive to soften or melt when heated to temperatures above ambient and then cure into an infusible cross-linked state; heating said resin coated particles such that said resin fuses and unites at contact areas between contiguous particles to form a porous matrix having interstices of a predetermined size when said resin has cured, with said porous matrix affixing to said perforated pipe to define a prepacked resin bonded well liner; extracting said outer mold from said prepacked resin bonded well liner; introducing into a well bore said prepacked resin bonded well liner; and allowing the subterranean fluid to flow through said interstices of said porous matrix and into said first bore of said base pipe while restricting therethrough the passage of solid particulates of a size greater than said interstices. 